Lithography mask blank

ABSTRACT

A lithography mask blank used as a material for producing a lithography mask includes at least one thin film which is formed on a substrate and has a desired function. The blank has a nitrogen-containing thin film as the above-mentioned thin film and an ammonium ion production preventing layer for preventing production of ammonium ions, which is formed on the nitrogen-containing thin film or at least at a surface portion of the nitrogen-containing thin film and which is exposed on the surface of the lithography mask after the lithography mask is manufactured.

TECHNICAL FIELD

The present invention relates to a lithography mask blank serving as amaterial of lithography masks such as photomasks, electron beam masks,or X-ray masks for use in producing semiconductor devices and the likeand to the lithography mask and, in particular, relates to a halftonephase shift mask blank serving as a material of halftone phase shiftmasks being one example of photomasks and to the halftone phase shiftmask.

BACKGROUND ART

In the production of a semiconductor device, a transfer pattern isformed by, for example, irradiation of exposure light through aphotomask (reticle).

As such a photomask, a photomask comprising a transparent substrate anda light-shielding film pattern formed thereon has been conventionallyused. As a material of the light-shielding film, a chromium-basedmaterial (chromium alone, a material containing chromium and nitrogen,oxygen, carbon, or the like, or a layered film composed of thesematerial films) has been generally used.

Further, in recent years, phase shift masks have been put to practicaluse in order to improve the resolution of transfer patterns. Varioustypes (Levenson type, auxiliary pattern type, self-aligned type, etc.)of phase shift masks are known. Among them, a halftone phase shift masksuitable for high-resolution pattern transfer of holes and dots isknown.

In the halftone phase shift mask, a light-semitransmissive film patternhaving a phase shift of about 1800 is formed on a transparent substrateand the light-semitransmissive film is formed by a single layer ormultilayers. For example, the publication of Japanese Patent No. 2966369discloses a light-semitransmissive film pattern which is formed by athin film made of a substance containing metal such as molybdenum,silicon, and nitrogen as main components.

The light-semitransmissive film made of such a material can control apredetermined phase shift amount and transmittance by a single layer andfurther is excellent in acid resistance, light resistance, and so on.

As described above, as the film materials used in the photomasks, therehave been developed not a few materials containing nitrogen for variousreasons.

On the other hand, when pattern transfer is performed using a photomask(reticle), high-energy laser light is irradiated onto the photomask. Asa result, chemical reactions on the photomask surface are accelerated bythe laser irradiation. Therefore, formation of some deposits areaccelerated so that the deposits are produced and adhered on thephotomask as foreign substances. Ammonium sulfate has been confirmed asone of such deposits.

The photomask is genarally cleaned by the use of a sulfuric acid-basedcleanser in the final process. It is considered that sulfuric acid orsulfuric acid ions derived from the sulfuric acid-based cleanser used inthe cleaning process often remain on the photomask after the cleaning.Therefore, it is considered that reactions between the sulfuric acidions and ammonium ions produced for some reason are accelerated by thelaser irradiation so as to cause the production of the deposits.

Particularly, following finer formation of LSI patterns in recent years,the wavelength of exposure light sources (exposure light wavelength) hasbeen changing toward a shorter wavelength, i.e. from a current KrFexcimer laser (248 nm) to an ArF excimer laser (193 nm). Under thesecircumstances, in case where, a short-wavelength exposure light sourcesuch as the ArF excimer laser is used, the laser output becomes furtherhigher. As a result, the formation of the deposits problematically tendsto be readily accelerated so that the production of the foreignsubstances becomes more outstanding.

It is considered that a generation source of the ammonium ions is asubstance or an adhering substance existing in the atmosphere or derivedfrom a pellicle. However, as a result of researching thin films usingmaterials containing nitrogen which are used in photomasks as describedabove, it has been found that more ammonium ions (NH₄ ⁺) exist on thesurfaces of the thin films containing nitrogen than on the surfaces ofthin films containing no nitrogen. Therefore, it is considered that thenitrogen-containing thin film may contribute to the deposition ofammonium sulfate that can be a particle defect.

The present invention has been made in terms of the foregoing prior artproblems and has an object to provide a lithography mask which iscapable of reducing the production of ammonium ions caused by acomponent of a thin film, and a lithography mask blank which is capableof producing such a lithography mask.

Another object of the present invention is to provide a halftone phaseshift mask which is capable of reducing the production of ammonium ionscaused by a component of a thin film, and a halftone phase shift maskblank which is capable of producing such a halftone phase shift mask.

DISCLOSURE OF THE INVENTION

The present invention has the following aspects.

(First Aspect)

A lithography mask blank used as a material for manufacturing alithography mask and comprising at least one layer in the form of a thinfilm having a required function and formed on a substrate, comprises, atleast, a nitrogen-containing thin film as the foregoing thin film, andan ammonium ion production preventing layer for preventing production ofammonium ions, which is formed on the nitrogen-containing thin film orat least at a surface portion of the nitrogen-containing thin film andwhich is exposed on the surface of the lithography mask after thelithography mask is manufactured.

(Second Aspect)

In the lithography mask blank of the first aspect, the ammonium ionproduction preventing layer is a thin film containing less nitrogen thanthe nitrogen-containing thin film.

(Third Aspect)

In the lithography mask blank of the first aspect, the ammonium ionproduction preventing layer is formed by a heat treatment of thenitrogen-containing thin film.

(Fourth Aspect)

A photomask is manufactured using the photomask blank according to anyof the first to third aspects.

(Fifth Aspect)

A halftone phase shift mask blank used as a material for manufacturing ahalftone phase shift mask and comprising at least alight-semitransmissive film composed of one layer or multilayers, havinga required transmittance and phase shift amount, and formed on asubstrate, comprises, at least, a nitrogen-containing thin film as athin film forming the light-semitransmissive film, and an ammonium ionproduction preventing layer for preventing production of ammonium ions,which is formed on the nitrogen-containing thin film or at least at asurface portion of the nitrogen-containing thin film and which isexposed on the surface of the mask after the mask is manufactured.

(Sixth Aspect)

In the halftone phase shift mask blank of the fifth aspect, the ammoniumion production preventing layer is a thin film containing less nitrogenthan the nitrogen-containing thin film.

(Seventh Aspect)

In the halftone phase shift mask blank of the fifth aspect, thenitrogen-containing thin film contains at least silicon and nitrogen andthe ammonium ion production preventing layer contains at least siliconand oxygen.

(Eighth Aspect)

In the halftone phase shift mask blank of the fifth aspect, the ammoniumion production preventing layer is formed by a heat treatment of thenitrogen-containing thin film.

(Ninth Aspect)

A halftone phase shift mask is manufactured using the halftone phaseshift mask blank according to any of the fifth to eighth aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view for describing a halftone phase shift maskblank according to Example 1 of the present invention;

FIG. 2 is a sectional view for describing methods of manufacturinghalftone phase shift mask blanks according to Examples 3 and 4 of thepresent invention;

FIG. 3 is a diagram showing a relationship between the presence/absenceof an ammonium production preventing layer and an ammonium ionconcentration on the film surface in Example 1;

FIG. 4 is a diagram showing a relationship between a heat treatment timeand an ammonium ion concentration on the film surface in Example 3; and

FIG. 5 is a diagram showing a relationship between a heat treatment timeand an ammonium ion concentration on the film surface in Example 4.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be described in detail.

Based on the fact that, in a lithography mask blank such as a photomaskblank, ammonium ions are extracted on a nitrogen-containing thin filmwhose surface is exposed outside after a mask is manufactured, thepresent inventors have estimated that the production of ammonium ions iscaused by nitrogen in the film. Since it has been confirmed that eventhe nitrogen-containing thin film hardly contains ammonium ions therein,it is considered that the nitrogen component in the thin film causessome change in quality at the surface of the film to produce theammonium ions.

In the present invention, an ammonium ion production preventing layerfor preventing the production of ammonium ions is formed on anitrogen-containing thin film or at least at a surface portion of anitrogen-containing thin film to thereby prevent the production ofammonium ions on the film surface considered to be caused by nitrogen inthe film. In this manner, the production of ammonium ions considered tobe caused by nitrogen in the film is reduced in the layer whose surfaceis exposed outside after a mask is manufactured.

As a result, the ammonium ion concentration on the film surface isreduced so that even if sulfuric acid, sulfuric acid ions, or the likeremains in sulfuric acid cleaning of a mask blank thereafter, insulfuric acid cleaning of a photomask manufactured using a mask blankthereafter, it is possible to suppress the production of foreignsubstances such as ammonium sulfate caused by ammonium ions due to laserirradiation during exposure.

In the present invention, the surface after treated for preventing theproduction of foreign substances caused by ammonium ions from ammoniumsulfate or the like has the ammonium ion (NH₄ ⁺) concentration reducedas compared with that before the treatment, when the ammonium ion (NH₄⁺) concentration is measured by an ion chromatography method using purewater extraction or the like. For example, the treatment is performed sothat the NH₄ ⁺ concentration measured by the ion chromatography methodbecomes 20 ng/cm² or less, preferably 10 ng/cm² or less, and morepreferably 5 ng/cm² or less.

In the present invention, the formation of the ammonium ion productionpreventing layer is carried out so as not to impair the primary functionof the thin film. Alternatively, it is adjusted to have the primaryfunction when the ammonium ion production preventing layer is formed.

In the present invention, the formation of the ammonium ion productionpreventing layer can be carried out when or after a mask blank ismanufactured or when or after a mask is manufactured.

The following two methods are typically considered as ammonium ionproduction preventing layer forming methods.

(1) To provide a layer, on the outermost surface, containing a smallquantity of substance that causes the production of ammonium ions.

(2) To form at least the outermost surface as a layer that hardly elutesa substance causing the production of ammonium ions or a layer thatsuppresses the production of ammonium ions, even if such a substanceexists.

With respect to the method (1), there is, specifically, a method offorming a thin film (ammonium ion production preventing layer)containing less nitrogen than the nitrogen-containing thin film. Such anammonium ion production preventing layer is additionaly formed on thenitrogen-containing thin film. By covering the nitrogen-containing thinfilm with the thin film containing less nitrogen than thenitrogen-containing thin film, the presence of nitrogen on the surface,which is exposed outside after the mask is formed, becomes less. Thismakes it possible to prevent the production of ammonium ions on the thinfilm surface due to nitrogen in the thin film. It is noted here that thethin film containing less nitrogen includes a thin film containingsubstantially no nitrogen.

With respect to the method (2), there is specifically cited, forexample, a heat treatment of the nitrogen-containing thin film. Bycarrying out the heat treatment in the atmosphere, an atmospherecontaining oxygen in the form of O₂, CO₂, or the like, an atmosphere ofinert gas such as nitrogen or Ar, a vacuum, or the like, thenitrogen-containing thin film of the mask blank and its surface layerportion are subjected to thermal perturbation.

This accelerates rearrangement of the film structure so that, forexample, dangling bonds of silicon and nitrogen being thin film formingelements are efficiently combined at the film surface layer portion,thereby changing to a stable state.

On the other hand, depending on the atmosphere where the heat treatmentis performed, an extremely thin dense oxide film, for example, is formedthrough reactions between the film surface likewise subjected to thethermal perturbation and the atmosphere, thereby also satisfying theforegoing method (1).

That is, by the proper application of thermal energy, the photomasksurface is changed in quality to a chemically more stable state. Thismakes it possible to suppress the production of ammonium ions on thethin film surface.

In order to achieve such a preferable action, the heat treatmenttemperature is preferably 180° C. or higher, and more preferably 250° C.or higher.

Although depending on a treatment temperature and a treatmentatmosphere, the heat treatment time is 5 minutes or more at minimum, andpreferably 10 minutes or more in consideration of uniformly applying thethermal perturbation to the photomask blank and stably controlling thechange in quality inside the thin film.

When the heat treatment temperature exceeds 400° C., in an activeatmosphere containing oxygen, for example, reaction with the thin filmsurface may drastically proceed to impair the function of the thin film,which thus should be taken into account.

In the case of the heat treatment at high temperatures, it is preferablethat the heat treatment be carried out in an atmosphere containing nooxygen or where the oxygen concentration is fully controlled.

As a method other than the foregoing heat treatment, such a method mayalso be considered wherein a substance for suppressing the production ofammonium ions due to nitrogen coexists with nitrogen in the film.Oxygen, for example, is cited as such a substance that suppresses theproduction of ammonium ions, while, as a method of forming such anammonium ion production preventing layer, there is a method ofimplanting oxygen ions or the like into the surface of thenitrogen-containing thin film or a method of performing a surfacetreatment such as a surface oxidation treatment using heat, plasma, orthe like.

In the present invention, foreign substances caused by ammonium ionscomprises ammonium sulfate, ammonium salt containing ammonium sulfate asa main component, other ammonium salts, and so on.

In the present invention, as a thin film having a required function in aphotomask blank, use is made of, for example, a light-shielding film, areflection preventing film, a light-semitransmissive film for a halftonephase shift mask, or the like. Such a thin film often corresponds to athin film whose surface is exposed outside after a photomask ismanufactured.

A halftone phase shift mask blank in the present invention comprises, atleast, a nitrogen-containing thin film as a thin film forming alight-semitransmissive film, and an ammonium ion production preventinglayer for preventing the production of ammonium ions, which is formed onthe nitrogen-containing thin film or at least at a surface portion ofthe nitrogen-containing thin film and whose surface is exposed outsideafter the mask is manufactured.

When the nitrogen-containing thin film is the light-semitransmissivefilm, having a required transmittance and phase shift amount, of thehalftone phase shift mask blank as described above, thenitrogen-containing thin film represents a light-semitransmissive filmof a single-layer structure composed of the nitrogen-containing thinfilm or a nitrogen-containing thin film, of a light-semitransmissivefilm of a multilayer structure, formed just under the ammonium ionproduction preventing layer.

Herein, as a material of the light-semitransmissive film of thesingle-layer structure, use is made of, for example, a materialcontaining silicon and nitrogen, a material containing metal, silicon,and nitrogen, or a material containing, in addition thereto, at leastone selected from oxygen, fluorine, carbon, and hydrogen. As the metal,use is made of at least one selected from molybdenum, tantalum,tungsten, chromium, titanium, nickel, palladium, hafnium, zirconium.

Such a material film can be formed by implementing reactive sputteringin an atmosphere of reactive gas such as nitrogen by the use of a targetmade of silicon, or metal and silicon, while it can also be formed usinga target containing nitrogen and so on.

As the light-semitransmissive film of the multilayer structure, use ismade of a film in which the material films each forming thelight-semitransmissive film of the single-layer structure are stacked intwo or more layers or a film comprising a transmittance adjusting layersuch as a metal film containing at least one selected from chromium,tantalum, hafnium, magnesium, aluminum, titanium, vanadium, yttrium,zirconium, niobium, molybdenum, tin, lanthanum, tungsten, silicon andthe foregoing single-layer material (halftone film) which are stacked inlayers. In order to achieve an effect as a halftone phase shift film,the light-semitransmissive film has a phase difference set to about 180°and a transmittance is set to a value selected from a range of 3 to 40%.

Particularly, when the ammonium ion production preventing layer isformed on the material layer containing metal, silicon, and nitrogen orthe material layer containing, in addition thereto, at least oneselected from oxygen, fluorine, carbon, and hydrogen, use can be madeof, as a material of the ammonium ion production preventing layer, amaterial containing silicon and oxygen or a material containing, inaddition thereto, one kind selected from metal, nitrogen (less amount ofnitrogen as compared with the nitrogen-containing layer), and carbon.

Hereinbelow, the present invention will be described in further detailusing examples.

EXAMPLE 1

Three halftone phase shift mask blanks were prepared in each of which alight-semitransmissive film 2 (film thickness: about 935 angstroms) ofnitrided molybdenum and silicon (MoSiN) was formed on a transparentsubstrate 1 by reactive sputtering (DC sputtering) in a mixed gasatmosphere of argon (Ar) and nitrogen (N₂) (Ar:N₂=10%:90%, pressure: 0.2Pa) using a mixture target of molybdenum (Mo) and silicon (Si)(Mo:Si=20:80 mol %) (see (1) in FIG. 1). Each halftone phase shift maskblank had a transmittance of 5.5% and a phase shift of about 180° withrespect to a KrF excimer laser (wavelength: 248 nm).

On the light-semitransmissive films 2 of the two phase shift blanks,ammonium ion production preventing layers 3 (thickness: about 30angstroms and 100 angstroms, respectively) each in the form of a thinfilm of oxidized molybdenum and silicon (MoSiO) were formed by reactivesputtering (DC sputtering) in a mixed gas atmosphere of argon (Ar) andoxygen (O₂) (Ar:O₂=60%:40%, pressure: 0.2 Pa) using the same target asdescribed above, respectively, thereby manufacturing halftone phaseshift mask blanks (see (2) in FIG. 1).

Each of these halftone phase shift mask blanks may have alight-semitransmissive film in the form of a MoSiN film+a MoSiO film.

FIG. 3 shows the results of measuring, by the ion chromatography method,ammonium ion concentrations on the film surfaces in the sample notapplied with the processing for preventing the production of foreignsubstances such as ammonium sulfate caused by ammonium ions (indicatedas “None” in the figure) and the samples applied with the processing forpreventing the production of foreign substances such as ammonium sulfatecaused by ammonium ions (indicated in terms of film thickness in thefigure). As clear from this figure, it is understood that ammonium ionson the film surface are remarkably reduced with respect to the samplesapplied with the ammonium sulfate production preventing process.

Then, after forming a chromium-based light-shielding film on the thinfilm in the form of the MoSiO film, a resist film was formed and aresist pattern was formed by pattern exposure and development. Then, theMoSiO film and the MoSiN film were etched by dry etching using CF₄+O₂gas and, after removing the resist, each sample was cleaned with 98%sulfuric acid (H₂SO₄) at 100° C. and rinsed with pure water. Thus, phaseshift masks were obtained.

With respect to each of these phase shift masks, since the sampleapplied with the processing for preventing the production of foreignsubstances such as ammonium sulfate caused by ammonium ions has lessammonium ions on the film surface, it is possible to reduce theproduction of foreign substance defect caused by ammonium sulfate whenpattern transfer is performed by laser irradiation using a KrF excimerlaser or the like.

EXAMPLE 2

Three halftone phase shift mask blanks were prepared in each of which alight-semitransmissive film 2 (film thickness: about 800 angstroms) ofnitrided molybdenum and silicon (MoSiN) was formed on a transparentsubstrate 1 by reactive sputtering (DC sputtering) in a mixed gasatmosphere of argon (Ar) and nitrogen (N₂) (Ar:N₂=10%:90%, pressure: 0.2Pa) using a mixture target of molybdenum (Mo) and silicon (Si)(Mo:Si=8:92 mol %) (see (1) in FIG. 1). Each halftone phase shift maskblank had a transmittance of 5.5% and a phase shift of about 180° withrespect to an ArF excimer laser (wavelength: 193 nm).

Two halftone phase shift mask blanks were prepared in each of which thelight-semitransmissive film 2 (film thickness: about 800 angstroms) ofnitrided molybdenum and silicon (MoSiN) was formed on the transparentsubstrate 1 that was the same as that in Example 1.

On the light-semitransmissive films 2 of the phase shift blanks,ammonium ion production preventing layers 3 (thickness: about 30angstroms and about 100 angstroms, respectively) each in the form of athin film of SiON were formed by reactive sputtering (DC sputtering) ina mixed gas atmosphere of argon (Ar), nitrogen (N₂), and oxygen (O₂)(Ar:N₂:O₂=20%:60%:20%, pressure: 0.1 Pa) using a silicon target,respectively. Thus, halftone phase shift mask blanks were produced. Itis noted here that the composition of the MoSiN layer isMo:Si:N=5:45:50at%, while the composition of the SiON layer isSi:O:N=42:43:15at%. Therefore, the content of nitrogen is smaller in“the ammonium ion production preventing layer” than in “thenitrogen-containing layer”.

Each of these halftone phase shift mask blanks may have alight-semitransmissive film in the form of a MoSiN film+a SiON film.

As a result of measuring ammonium ion concentrations on the filmsurfaces in these halftone phase shift mask blanks by the ionchromatography method, it was 3.5 ng/cm² with respect to the sample withthe film thickness of 30 angstroms while it was 2.8 ng/cm² with respectto the sample with the film thickness of 100 angstroms.

Then, after forming a chromium-based light-shielding film on the thinfilm in the form of the SiON film, a resist film was formed and a resistpattern was formed by pattern exposure and development. Subsequently,the SiON film and the MoSiN film were etched by dry etching using CF₄+O₂gas and, after removing the resist, each sample was cleaned with 98%sulfuric acid (H₂SO₄) at 100° C. and rinsed with pure water. Thus, phaseshift masks were obtained.

With respect to each of these phase shift masks, since the sampleapplied with the processing for preventing the production of foreignsubstances such as ammonium sulfate caused by ammonium ions has lessammonium ions on the film surface, it is possible to reduce theproduction of foreign substance defect caused by ammonium sulfate whenpattern transfer is performed by laser irradiation using a ArF excimerlaser or the like.

In the present invention, in order to remarkably reduce ammonium ions onthe film surface, the thickness of the ammonium production preventinglayer is preferably 10 angstroms or more, and more preferably 30angstroms or more.

EXAMPLE 3

Like in Example 1, a light-semitransmissive film (film thickness: about935 angstroms) 2 of nitrided molybdenum and silicon (MoSiN) was formedon a transparent substrate 1 (see (1) in FIG. 2).

Then, a heat treatment 4 was carried out at 280° C. in the atmosphere(see (2) in FIG. 2). FIG. 4 shows the result of measuring, by the ionchromatography method, a relationship between a heat treatment time andan ammonium ion concentration on the film surface.

As clear from FIG. 4, it has been found that ammonium ions are reducedby the heat treatment and, particularly when the heat treatment timeexceeds 15 minutes or so, the ammonium ions are remarkably reduced. Thisis because it is considered that, in this example, thermal perturbationapplied to the mask blank is uniformly and effectively exerted over thewhole surface of the thin film after the lapse of about 15 minutes fromthe start of the heat treatment.

Next, the mask processing like in Example 1 was carried out to therebyobtain a phase shift mask.

With respect to this phase shift mask, since the sample applied with theammonium sulfate production preventing process had less ammonium ions onthe film surface, it was possible to reduce the production of foreignsubstance defect caused by ammonium sulfate when pattern transfer wasperformed by laser irradiation using a KrF excimer laser or the like.

EXAMPLE 4

Like in Example 1, a light-semitransmissive film (film thickness: about935 angstroms) 2 of nitrided molybdenum and silicon (MoSiN) was formedon a transparent substrate 1 (see (1) in FIG. 2).

Then, a heat treatment 4 was carried out at 400° C. in a nitrogenatmosphere (see (2) in FIG. 2). FIG. 5 shows the result of measuring aheat treatment time and an ammonium ion concentration on the filmsurface by the ion chromatography method.

As clear from FIG. 5, it has been found that ammonium ions are reducedby the heat treatment and, particularly when the heat treatment timeexceeds 20 minutes or so, the ammonium ions are remarkably reduced. Thisis because it is considered that, in this example, thermal perturbationapplied to the photomask blank is uniformly and effectively exerted overthe whole surface of the thin film after the lapse of about 20 minutesfrom the start of the heat treatment.

Then, the mask processing like in Example 1 was carried out to therebyobtain a phase shift mask.

With respect to this phase shift mask, since the sample applied with theammonium sulfate production preventing process had less ammonium ions onthe film surface, it was possible to reduce the production of foreignsubstance defect caused by ammonium sulfate when pattern transfer wasperformed by laser irradiation using a KrF excimer laser or the like.

INDUSTRIAL APPLICABILITY

According to the present invention, a thin film whose surface is exposedoutside after a photomask is manufactured is a thin film containing atleast nitrogen, and the surface of the nitrogen-containing thin film isapplied with the processing for preventing the production of foreignsubstances such as ammonium sulfate caused by ammonium ions. As aconsequence, it is possible to obtain a photomask blank enabling theproduction of a photomask that does not deposit ammonium sulfate uponlaser irradiation.

1. A lithography mask blank used as a material for manufacturing alithography mask and comprising at least one layer of a thin film havinga required function and formed on a substrate, comprising: anitrogen-containing thin film as said thin film, and an ammonium ionproduction preventing layer for preventing production of ammonium ions,which is formed on said nitrogen-containing thin film or at least at asurface portion of said nitrogen-containing thin film and which isexposed on the surface of said lithography mask after said lithographymask is manufactured.
 2. A lithography mask blank according to claim 1,wherein: said ammonium ion production preventing layer is a thin filmcontaining less nitrogen than said nitrogen-containing thin film.
 3. Alithography mask blank according to claim 1, wherein: said ammonium ionproduction preventing layer is formed by a heat treatment of saidnitrogen-containing thin film.
 4. A photomask, wherein: the photomask ismanufactured using said lithography mask blank according to any ofclaims 1 to
 3. 5. A halftone phase shift mask blank used as a materialfor manufacturing a halftone phase shift mask and comprising at least alight-semitransmissive film composed of one layer or multilayers, havinga required transmittance and phase shift amount, and formed on asubstrate, comprising: a nitrogen-containing thin film as a thin filmforming said light-semitransmissive film, and an ammonium ion productionpreventing layer for preventing production of ammonium ions, which isformed on said nitrogen-containing thin film or at least at a surfaceportion of said nitrogen-containing thin film and which is exposed onthe surface of said mask after said mask is manufactured.
 6. A halftonephase shift mask blank according to claim 5, wherein: said ammonium ionproduction preventing layer is a thin film containing less nitrogen thansaid nitrogen-containing thin film.
 7. A halftone phase shift mask blankaccording to claim 6, wherein: said nitrogen-containing thin filmcontains at least silicon and nitrogen and said ammonium ion productionpreventing layer contains at least silicon and oxygen.
 8. A halftonephase shift mask blank according to claim 5, wherein: said ammonium ionproduction preventing layer is formed by a heat treatment of saidnitrogen-containing thin film.
 9. A halftone phase shift mask, wherein:said halftone phase shift mask is manufactured using said halftone phaseshift mask blank according to any of claims 5 to 8.